This invention pertains to the communication art and, in particular, to an automatic noise limiter for use in a radio receiver.
Automatic noise limiter circuits, especially those used in radio receivers, are well known in the communication art. In radio receiver applications the function of the noise limiter is to detect noise signals, e.g. those signals exceeding a predetermined threshold level, and limit the noise signals to a given level. Thus, the audio effect of the noise limiter is to minimize noise impulses or bursts which would otherwise be reproduced by the receiver.
Prior art noise limiter circuits, especially those used in amplitude modulated receivers, have proved less than satisfactory. Generally, such noise limiter circuits have either been very sophisticated and, therefore, expensive to manufacture requiring large numbers of costly components, or they have been very primitive both in structure and in operation. Ideally, an automatic noise limiter circuit for use in an amplitude modulated receiver should limit all signals which exceed a given percent modulation figure, commonly 100% modulation, since this represents the known level of audio broadcast from the transmitter. Heretofore, inexpensively and easily manufactured noise limiter circuits for amplitude modulated receivers have not adequately provided limiting in response to the desired percent modulation level.